Modern high performance optical systems often require actively controlled optical components to provide beam pointing and line-of-sight stabilization. In high-energy laser applications, it is commonplace to use a DM to improve laser beam quality, and correct for atmospheric disturbances.
FIG. 1 illustrates a conventional DM, which is a thin, flexible mirror used to reflect light rays at measured angles, for performing high-order distortion correction. Conventional DM 100 includes deformable face sheet 101 having mirror surface 102 coated thereon. A plurality of electrostrictive actuators 104 are in physical contact with a reverse surface of deformable face sheet 101, at various locations. Conventional DM 100 also includes backplane assembly 105, upon which electrostrictive actuators 104 are affixed. Using a control system to adjust the voltage applied to individual electrostrictive actuators, conventional DM 100 displaces deformable face sheet 101 by a controlled amount, on the order of a few microns, deforming mirror surface 102 into a desired shape.
In complex modern optical systems used for observational purposes, such as the Hubble Space Telescope (“HST”), James Webb Space Telescope (“JWST”) or other space-borne telescopes, conventional DMs are used to correct for residual optical imperfections caused during the manufacturing, assembly, and alignment processes. In addition to conventional DMs, however, these modern optical systems often include additional mirrors, such as steering and stabilization mirrors, which perform additional functions. As the number of electromechanical devices and reflective surfaces are increased, system weight and complexity increase, resulting in an overall decrease in mission capability.
A second problem inherent to conventional DMs is their extremely limited range of motion, owing to the practical considerations of the actuation systems that are employed to “bend” the mirror surface. In this regard, conventional DMs must be installed and aligned with great precision so that they can operate within normal limitations and specified operating parameters. Conventional DMs must therefore also be used in conjunction with other controllable mirrors to accommodate the alignment, steering and stabilization functions.
Conventional DMs are often used in directed energy systems which can take advantage of the large number of photons available in a beam path to permit sensing of the wavefront error at high bandwidth and correct it with the DM. With conventional DMs, even if plurality of electrostrictive actuators 104 are somewhat non-linear, the wavefront error sensing can be done at such a high bandwidth that the mirror can be driven to accurately correct the wavefront. Because a subsequent wavefront error measurement may not occur immediately, in low-light applications, once a wavefront error is detected and the mirror is commanded to deform in a precise manner, a conventional mirror may not be able to achieve the commanded shape through actuator response alone.
To actively control beam steering, high performance optical systems often use conventional FSMs, which effectuate line-of-sight beam stabilization, in conjunction with a separate DM. FIGS. 2 and 3 depict side and top views, respectively, of a conventional FSM, such as a LOCKHEED MARTIN® Kinematic Drive Design FSM. As illustrated, conventional FSM 200 typically includes mirror substrate 201, including mirror surface 202 coated thereon. Conventional FSM 200 also includes base plate 205, upon which mirror substrate 201 is affixed. A plurality of fast steering actuators, including fast steering actuators 206, 307, and 309, are positioned equidistantly around the periphery of base plate 205.
A plurality of two-axis flexures, including two-axis flexure 210, are in physical communication with and between each fast steering actuator and base plate 205, for steering the conventional FSM. Conventional FSM 200 further includes a plurality of U-shaped flexures, including U-shaped flexures 211, 312 and 314, positioned equidistantly from each other around the periphery of backplane assembly 205, for supporting mirror substrate 201, where each U-shaped flexure is positioned directly across backplane assembly 205 from fast steering actuators 206, 307 and 309.
One problem associated with high bandwidth FSMs used for beam stabilization is that extraordinary care and design innovation are required in order to achieve bandwidths approaching 1 kHz. Even with the most advanced engineering techniques, FSMs must be installed very accurately to approach the 1 kHz practical bandwidth limit for large (i.e. aperture size greater than 20 cm) beam stabilization (or de-jitter) mirrors.
When conventional FSMs are built with a high bandwidth capability, they have a very limited angular range. Therefore, conventional FSMs typically have to be used with a lower bandwidth, wider angle range companion mirror so that the line of sight of the optical system may be steered over an appreciable angle.
Since conventional adaptive optical systems typically use separate, heavy, large and complex mirrors for large angle motion, high bandwidth tip/tilt and phase correction, it is considered highly desirable to provide an adaptive optical system which overcomes the deficiencies of conventional FSMs and DMs. In particular, it is desirable to provide a hybrid adaptive optical system capable of both providing high-bandwidth beam stabilization and wide angle steering capabilities like an FSM, with the ability to correct optical aberrations like a DM.